The speed of a microprocessor unit (MPU) has recently been remarkably increased. At present, the working frequency reaches not less than several GHz, and is in the process of further speed increase. Speed increase of the MPU is realized by increasing the integration density, and hence the heat generation density is inevitably increased. In the MPU having the maximum speed at present, the total heat generation amount reaches not less than 100 W and the heat generation density reaches not less than 400 W/mm2, and the heat generation amount is also continuously increased due to further speed increase.
In some cases, a fan or a water cooler is provided on the upper surface of the MPU package in order to cool the MPU. However, a heat generating section of the MPU is a circuit section formed on a silicon substrate. Cooling is performed through the package or the like, and hence the cooling efficiency is disadvantageously low.
Therefore, a structure obtained by forming a fluid channel on the silicon substrate of the MPU for circulating a fluid in the fluid channel is proposed. Cooling is enabled extremely in the vicinity of the semiconductor substrate generating heat, thereby coping with increase in heat generation following speed increase of the MPU. However, this water cooling system for the MPU employs an electroosmotic flow pump as a pump. Therefore, fluid channel resistance is increased in the narrow fluid channel formed on the silicon substrate of the MPU, and hence a high driving voltage of about 400 V is disadvantageously required.
While an electroosmotic flow is employed for flowing a solvent containing an analytical sample and electrophoresis or dielectrophoresis is employed for migrating sample particles in the solvent also in a microanalysis system (μTAS), this system directly applies an electric field to the solution, and hence the same is unsuitable for a sample denatured upon application of the electric field.
In consideration of the aforementioned conditions, it is understood that a fluid actuator driving a fluid with surface acoustic wave vibration is preferable. Patent Document 1, Non-Patent Document 1 and Patent Document 2 disclose fluid actuators employing surface acoustic waves.
Patent Document 1 discloses a micropump obtained by arranging surface wave generating means provided with interdigital (comb-shaped) electrodes on a piezoelectric element constituting a part of a fluid channel.
Non-Patent Document 1 discloses a fluid actuator having an interdigital electrode provided on a piezoelectric thin film for driving a fluid on a substrate by applying an AC voltage to the interdigital electrode to induce Lamb waves.
Patent Document 2 discloses an ink jet head provided with two piezoelectric substrates having a thickness generally equivalent to the wavelength of surface acoustic waves superposed with each other through a rib for forming a nozzle, and UDTs (unidirectional comb-shaped interdigital electrodes) respectively arranged on the surfaces of the piezoelectric substrates opposite to the nozzle for sequentially inputting one pulse waveform into the UDTs in an out-of-phase manner to drive the same, thereby generating back surface waves of surface acoustic waves on a wall surface forming the nozzle of the piezoelectric body, so that convex strain on the nozzle wall surface moves toward the forward end of the nozzle due to the back surface waves and the fluid in the nozzle is dragged by this convex strain to move toward the forward end and is ejected from the forward end of the nozzle as droplets.    Patent Document 1: Japanese Unexamined Utility Model Publication No. 03-116782    Patent Document 2: Japanese Unexampled Patent Publication No. 2002-178507    Non-Patent Document 1: R. M. Moroney et. al., “Microtransport induced by ultrasonic Lamb waves”, Appl. Phys. Lett. 59(7), E-E774-776, 1991